Thermoplastic film for a disposable container made of expandable thermoplastic particles

ABSTRACT

A foam thermoplastic container e.g. cup, bowl molded from expandable thermoplastic particles e.g. expandable polystyrene, has a film made of a thermoplastic resin e.g. solid polystyrene, rubber-modified polystyrene, PET, polyethylene, polypropylene, fused to its inner sidewall surface by heat and pressure to create a barrier to resist the leakage of liquid and food with oil and/or fatty components and to increase the rim strength of the container. The thermoplastic resin film can be fused to the outer surface of the container for printing purposes and/or to create a barrier and/or can be fused to the base surfaces of the container. The molding machine used to form the foam container is used to fuse the film to the container.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a disposable container. Moreparticularly, the present invention relates to a thermoplastic film,which is heat and pressure fused to the inner and/or outer surfaces ofthe sidewall of a thermoplastic container, and optionally, to the innerand/or outer surfaces of container's base. The container is generallypre-formed via a molding process from expandable thermoplasticparticles, e.g. expandable polystyrene particles (EPS). The container isused for holding liquids, such as coffee or foods containing oil and/orfat components such as precooked fat-containing foods, e.g. instantnoodles, soups, fried chicken, and the like.

2. Background Art

The manufacture of molded articles, such as containers, i.e. cups,bowls, etc. from expanded thermoplastic particles is well known. Themost commonly used thermoplastic particles are expandable polystyreneparticles known as EPS. Typically, polystyrene beads are impregnatedwith a blowing agent, which boils below the softening point of thepolystyrene and causes the impregnated beads to expand when they areheated.

The formation of molded articles from impregnated polystyrene beads isgenerally done in two steps. First, the impregnated polystyrene beadsare pre-expanded to a density of from about 2 to 12 pounds per cubicfoot. Second, the pre-expanded beads are heated in a closed mold tofurther expand the pre-expanded beads to form a fused article having theshape of the mold.

The expandable polystyrene particles used to make foam containers aregenerally prepared by an aqueous suspension polymerization process,which results in beads that can be screened to relatively precise beadsizes. Typically, bead diameters are within the range of from about0.008 to about 0.02 inch. Occasionally, cups are made from particleshaving bead diameters as high as 0.03 inches.

In spite of careful bead size control, one problem, which continues toplague the container industry, is that after a period of time the EPScontainers have a tendency to leak coffee or the oil and/or fatcomponents in food substances carried by the containers. That is, thecoffee or the oil and/or fat permeate around the fused polystyrene beadsonto the outer surface of the sidewall of the container. The result canbe an unsightly stain on the outer surface of the sidewall of thecontainer and/or inconvenience to the holder of the container.

Several approaches have evolved over the years directed toward thereduction of leakage in these containers for retaining liquids and/orpre-cooked foods.

Amberg et al., U.S. Pat. No. 4,036,675 discloses a container made fromfoamed plastic material, preferably foamed polystyrene, which is linedon one or both sides with unoriented polyolefin film, preferablypolypropylene. The film is secured to the foamed plastic base materialusing as a heat-sensitive adhesive a vinylic polymer or polyamide resin.The film is coated with a wet adhesive and dried before laminating thefilm to the foam material. Laminating is done by heating the foammaterial to 250-275° F., preheating the coated film to 100-180° F., andpressing the coated film surface against the heated foam using a coldplaten or roller for 10 to 15 seconds.

Sonnenberg U.S. Pat. Nos. 4,703,065 and 4,720,419 disclose thermoplasticpolymer foam cups for retaining coffee that are molded fromthermoplastic polymer particles whose surfaces are coated with afluorosurfactant before molding.

Sonnenberg U.S. Pat. No. 4,785,022 discloses a method for enhancing thecoffee retention of molded foam cups, which involves coating theexpandable polystyrene particles with various rubber polymers andcopolymers. The rubber useful in the invention can be selected from thegroup consisting of polybutene, polyisobutylene, isobutylene-butenecopolymer and butene-ethylene copolymer.

Arch, et al. U.S. Pat. No. 4,798,749 approaches the problem of coffeeleakage by replacing conventional blowing agents such as butanes,n-pentane, hexanes, and the halogenated hydrocarbons with isopentane inthe expandable styrene polymer particles.

Ikeda, et al., U.S. Pat. No. 4,698,367 discloses expandablethermoplastic resin particles in which the thermoplastic resin in whicha copolymer composed of a fluorinated vinyl polymer part and ahydrophilic vinyl polymer part covers or is included on the surface orin the surface layer of the expandable thermoplastic particle. Theseresin particles are useful for producing package containers for oily orfatty foods.

Sakoda et al., U.S. Pat. No. 6,277,491 B1 is directed to the preventionof oil from penetrating into a vessel obtained from expandablethermoplastic resin beads through molding. This is achieved by coatingthe surface of the resin beads or incorporating the resin beads with afluorine-containing block copolymer comprising a fluorine-containingvinyl-type polymer segment derived from a fluorine-containing vinyl-typemonomer and a lipophilic vinyl-type polymer segment derived from alipophilic vinyl-type monomer.

The containers of the above prior art are generally addressed topolystyrene containers, such as cups or bowls. The following patentspertain to paper cups that are either spray coated or that contain athermoplastic resin film either for heat insulating purposes or forproducing a high impermeability to liquids.

For example, Suzuki et al., U.S. Pat. No. 4,206,249 discloses a processfor producing a paper container having high impermeability to liquidwhich comprises spray coating a polymerizable solution containing aprepolymer onto a wall surface of a previously fabricated papercontainer and irradiating the coated wall with ultraviolet light toeffect the setting of the prepolymer on the wall surface of thecontainer. This forms a coating, which is impermeable to liquids, suchas water, milk, soft drinks, oils, etc. This '249 patent also teaches incolumn 2, lines 45-62, that there is a lining method in which theinterior wall surface of the container is lined with a thermoplasticfilm. The thermoplastic film is first laminated onto a blank and theblank is formed into a container.

Iioka, U.S. Pat. No. 4,435,344 discloses a heat-insulating papercontainer where the outer and inner surfaces of the body member areextrusion coated or laminated with a thermoplastic synthetic resin film.The resin film is converted into a foamed layer on the paper substrateand then the container is formed. The result is a container with goodthermo-insulation properties. This film preferably is polyethylene butas taught in column 3, lines 50 - 55, this resin film can bepolypropylene, polyvinyl chloride, polystyrene, polyester, nylon and thelike.

Iioka et al., U.S. Pat. No. 5,490,631 discloses a heat insulating papercontainer comprising a body member wherein a thick foamed heatinsulating layer is made of a thermoplastic synthetic resin film isformed in the printed area of the outer surface and a less thick foamedheat-insulating layer that can be made of the same thermoplasticsynthetic resin film is formed in the non-printed area of the outersurface. The thermoplastic synthetic resin film is typicallypolyethylene.

Breining, et al., U.S. Pat. No. 6,416,829 B2 discloses a heat insulatingpaper cup where the body member is coated on its outside surface with afoamed low density polyethylene, and on its inside surface with anunfoamed modified low density polyethylene.

None of the containers of the prior art have a thin thermoplastic filmfused to the inner and/or outer surfaces of a foam molded container forretaining food items such as coffee, soups, meats, and the like for thepurpose of reducing the penetration of the liquid and/or the oil orfatty components in these food items through the foam container.

SUMMARY OF THE INVENTION

The invention relates to a container suitable for use in retaining hotliquids such as coffee or water added to food items such as instantsoups and/or stews. A foam molded container made from expandablethermoplastic particles is formed and an extruded or blown thinthermoplastic film is encircled at least around the inside of thecontainer, and the film is heat fused onto the inner surface of thesidewall of the container. Optionally, a thin thermoplastic film can beencircled around and heat fused onto the outer surface of the sidewallof the container, and optionally, a film can be heat fused to the innerand/or outer surfaces of the base of the container. The resultantcontainer is impervious to leakage and/or stains caused by liquidsand/or oily and fatty foods. The film around the outer surface of thesidewall of the container can also be used for labeling and printingpurposes.

The thermoplastic film is made of a polymer selected from the groupconsisting of solid polystyrene, rubber modified polystyrene, polymethylmethacrylate, rubber-modified polymethyl methacrylate, polypropylene,polyethylene, polyethylene terephthalate (PET), and mixtures thereof.Additionally, one or more of these polymers can be blended with astyrene/maleic anhydride copolymer.

In the preferred embodiments of the invention, the polymer for thethermoplastic film is selected from the group consisting of solidpolystyrene and rubber-modified polystyrene, i.e. a medium impactpolystyrene resin and a high impact polystyrene resin. The high impactpolystyrene appears to give the best results. The thickness of thethermoplastic film ranges from about 0.10 mil to about 5.0 mils, andpreferably is about 1.0 mil, and extends substantially the depth of thecontainer around the inner and/or outer surfaces of the sidewall of thecontainer.

Preferably, the thermoplastic film is fused to the inner and/or outersurfaces of the sidewall of the foam container via the same moldingequipment used to form the foam container. The thermoplastic film canoptionally be fused to the inner and/or outer surfaces of the base ofthe formed container.

The foam molded container is made of expandable thermoplastic resinbeads, and in the preferred embodiments, this expandable thermoplasticresin is expandable polystyrene particles (EPS).

It is an object of the present invention to provide a thermoplastic foamcontainer that exhibits improved resistance to leakage and/or stain, andimproved mechanical properties, such as improved rim strength andsurface hardness of the container.

It is a further object of the present invention to provide athermoplastic film fused to at least the inner surface of the sidewallof a formed foam container by heat and pressure, and optionally can befused to the outer surface of the sidewall and/or to the surfaces of thebase of the container.

It is still a further object of the present invention to provide athermoplastic container that is suitable for receiving hot liquids, suchas coffee, hot water for instant soups, stews, etc. and whichthermoplastic container with its contents can be reheated in amicrowave.

DETAILED DESCRIPTION OF THE INVENTION

In the invention, a foam container, e.g., cups, bowls, and the like ismolded from expandable thermoplastic particles. These expandablethermoplastic particles are made from any suitable thermoplastichomopolymer or copolymer. Particularly suitable for use are homopolymersderived from vinyl aromatic monomers including styrene,isopropylstyrene, alpha-methylstyrene, nuclear methylstyrenes,chlorostyrene, tert-butylstyrene, and the like, as well as copolymersprepared by the copolymerization of at least one vinyl aromatic monomerwith monomers such as divinylbenzene, butadiene, alkyl methacrylates,alkyl acrylates, acrylonitrile, and maleic anhydride, wherein the vinylaromatic monomer is present in at least 50% by weight of the copolymer.Styrenic polymers are preferred, particularly polystyrene. However,other suitable polymers may be used, such as polyolefins (e.g.polyethylene, polypropylene), and polycarbonates (polyphenylene oxides,and mixtures thereof.

In the preferred embodiments, the expandable thermoplastic particles areexpandable polystyrene (EPS) particles. These particles can be in theform of beads, granules, or other particles convenient for the expansionand molding operations. Particles polymerized in an aqueous suspensionprocess are essentially spherical and are preferred for molding the foamcontainer of the invention. These particles are screened so that theirsize ranges from about 0.008 to about 0.02 inch.

These expandable thermoplastic particles are impregnated using anyconventional method with a suitable blowing agent. For example, theimpregnation can be achieved by adding the blowing agent to the aqueoussuspension during the polymerization of the polymer, or alternatively byre-suspending the polymer particles in an aqueous medium and thenincorporating the blowing agent as taught in U.S. Pat. No. 2,983,692 toD. Alelio. Any gaseous material or material which will produce gases onheating can be used as the blowing agent. Conventional blowing agentsinclude aliphatic hydrocarbons containing 4 to 6 carbon atoms in themolecule, such as butanes, pentanes, hexanes, and the halogenatedhydrocarbons, e.g. CFC's and HCFC'S, which boil at a temperature belowthe softening point of the polymer chosen. Mixtures of these aliphatichydrocarbons blowing agents can also be used.

Alternatively, water can be blended with these aliphatic hydrocarbonsblowing agents or water can be used as the sole blowing agent as taughtin U.S. Pat. Nos. 6,127,439; 6,160,027; and 6,242,540 assigned to NOVAChemicals (International) S.A. In these patents, water-retaining agentsare used. The weight percentage of water for use as the blowing agentcan range from 1 to 20%. The texts of U.S. Pat. Nos. 6,127,439,6,160,027 and 6,242,540 are incorporated herein by reference.

The impregnated thermoplastic particles are generally pre-expanded to adensity of from about 2 to about 12 pounds per cubic food. Thepre-expansion step is conventionally carried out by heating theimpregnated beads via any conventional heating medium, such as steam,hot air, hot water, or radiant heat. One generally accepted method foraccomplishing the pre-expansion of impregnated thermoplastic particlesis taught in U.S. Pat. No. 3,023,175 to Rodman.

The impregnated thermoplastic particles can be foamed cellular polymerparticles as taught in Arch et al. U.S. patent application Ser. No.10/021,716 assigned to NOVA Chemicals Inc, the teachings of which areincorporated herein by reference. The foamed cellular particles arepreferably polystyrene that are pre-expanded to a density of from about12.5 to about 34.3 pounds per cubic foot, and contain a volatile blowingagent level less than 6.0 weight percent, preferably ranging from about2.0 wt % to about 5.0 wt %, and more preferably ranging from about 2.5wt % to about 3.5 wt % based on the weight of the polymer.

In a conventional manner, the pre-expanded particles or “pre-puff” areheated in a closed mold to further expand the pre-puff and to form thecontainer of the invention.

The thermoplastic film is made of a polymer selected from the groupconsisting of solid polystyrene, rubber modified polystyrene, polymethylmethacrylate, rubber-modified polymethyl methacrylate, polypropylene,polyethylene, polyethylene terephthalate (PET), and mixtures thereof.Additionally, one of the preceding polymers can be blended with astyrene/maleic anhydride copolymer. In the preferred embodiments of theinvention, the polymer for the thermoplastic film is selected from thegroup consisting of solid polystyrene and rubber-modified polystyrene,i.e. a medium impact polystyrene resin and a high impact polystyreneresin.

Polystyrene is a high molecular weight linear polymer produced bypolymerizing styrene. When made from only the styrene monomer, theresulting polymer has a glass transition temperature of about 100° C.and is brittle, showing very poor strength i.e. elongation to rupturecharacteristics. It is known that the strength characteristics can beimproved by incorporating rubber modifiers, such as butadiene rubber,which product is referred to as a medium impact polystyrene or a highimpact polystyrene (HIPS), depending on the weight percent of rubberpolymer incorporated into the styrene. For the medium impactpolystyrene, the polystyrene ranges from about 95 to 98 weight percentand the rubber polymer ranges from about 2 to about 5 weight percent,based on the weight of the polystyrene resin. For the high impactpolystyrene, the polystyrene ranges from about 85 to about 95 weightpercent and the rubber polymer ranges from about 5 to about 15 weightpercent, based on the weight of the polystyrene resin.

The process for making “HIPS” is well known to those skilled in the art.Such known processes are exemplified in U.S. Pat. No. 3,903,202 and U.S.Pat. No. 4,146,589, the teachings of which are incorporated herein byreference. The rubber is “dissolved” in the styrene monomer (actuallythe rubber is infinitely swollen with the monomer). The resulting“solution” is fed to a reactor and with the use of a suitable initiatorsystem polymerization occurs typically under shear. During thepolymerization, the styrene is grafted to the rubber. The grafting isthought to be necessary to provide the higher modulus and impactstrength, as compared to simple blends of polystyrene and butadienerubbers. When the conversion of the styrene is about equal to the weightpercent of the rubber in the system the phases invert, i.e. thestyrene/styrene polymer phase becomes continuous and the rubber phasebecomes discontinuous. After phase inversion the polymer is finished ina manner essentially similar to that for finishing polystyrene.

Preferably, the amount of rubber used in the high impact polystyrenefilm of the invention is about 8 weight percent and that used in mediumimpact polystyrene film is about 3 weight percent, based on the weightof the polystyrene resin.

Suitable rubbers for modifying the polystyrene are natural rubber,polybutadiene and its copolymers with styrene or other comonomers, i.e.styrene-butadiene copolymer rubber, polyisoprene and its copolymers withstyrene or other comonomers, acrylic rubbers, EPDM rubbers, polybutyleneand so on. Preferably, the rubber is polybutadiene or styrene-butadienecopolymer rubber.

The particle distribution of the rubber in the polystyrene matrix ispreferably unimodal. The average rubber particle size ranges from about0.5 microns to about 8 microns in size; preferably from about 1.0 micronto about 2.5 microns, more preferably from about 1 to about 2.0 micron;and most preferably from about 1.5 micron to about 2.0 microns. As isknown to those skilled in the art, the particle size of the rubberparticles are generally controlled by the applied shear rate, heat,pressure, or a combination of these factors, during the stage ofinversion of the polymerization when polystyrene becomes the continuousphase.

Suitable rubber modified polystyrene particles are commerciallyavailable. Preferred among the commercial products of medium and highimpact polystyrene are 5500, 5210, 4211, all available from NOVAChemicals Inc., 5100 Bainbridge Boulevard, Chesapeake, Va. 23320.

The rubber modified polystyrene particles may be in bead or pellet formand may include the customary ingredients and additives, such aspigments, colorants, plasticizers, mold release agents, stabilizers,ultraviolet light absorbers, and so on. Typical pigments include,without limitation, inorganic pigments such as carbon black, zinc oxide,titanium dioxide, and iron oxide, as well as organic pigments such asquinacridone reds and violets and copper phthalocyanine blues andgreens.

In a further preferred embodiment of the invention, the thermoplasticfilm is comprised of general solid polystyrene, which also is availablefrom NOVA Chemicals Inc., Beaver Valley Plant, Monaca, Pa.

The thermoplastic film may be formed via an extrusion process or a blowmolding process. Molding conditions may be the same as conditionsusually employed for molding impact modified polystyrenes. Preferably,the thermoplastic film of the invention is extruded from a slot or acirculate die.

Preferably, the thermoplastic film has an IZOD impact value ranging fromabout 50 to about 100 J/M and an impact resistance greater than 1.0ft-lb/inch.

The thermoplastic container can be a polystyrene cup that is fabricatedby a conventional cup-forming machine that has an inner shell and anouter shell, for example, Cup Production MODEL 6-VLC-125 machine, madeby Autonational B.V.

In one embodiment of the invention, after the cup or cups are molded,the thermoplastic film is formed into a cylinder and inserted into thecup, which, in turn is carried by a mandrel. The inner shell is insertedinto the cup, and heat and pressure is applied to the thermoplastic filmto fuse the film to the inner surface of the sidewall of the cup. Thepressure for the inner shell against the thermoplastic film ranges fromabout 20 to about 80 pounds per square inch, preferably from about 30 toabout 50 pounds per square inch (psi).

The fabrication rate for the film fusing operation for a single machineproducing 10-ounce cups ranges from about 18 to 120 cups per minute.Several machines can be used to increase the production rate. Heat isapplied to the thermoplastic film by means of steam in order to melt thethermoplastic film and the adjacent polystyrene beads so that a cohesiveeffect occurs between the inner surface of the sidewall of the cup andthe thermoplastic film. The temperature and time for this cohesion tooccur may vary, for example, from about 60° C. to about 120° C. forabout 3 to about 20 seconds.

It has been found that the thermoplastic film also increases the rimstrength of the container, which, in effect, increases the overallstrength of the container. The rim strength is a measure of the forcerequired (in kilograms) to cause the rim to crumble a one-fourth inchdisplacement from the opened edge of the container.

Other embodiments of the invention involve the thermoplastic film beingfused to the inner and/or outer surfaces of the sidewall and/or fused tothe inner and/or outer surfaces of the base of the container.

The invention is further illustrated, but not limited by, the followingexamples wherein all parts and percentages are by weight unlessotherwise specified.

EXAMPLES Example 1

This example illustrates the preparation of thermoplastic film linedcontainers. The NOVA Chemicals F271TU (expandable polystyrene) cup beadsblended with zinc stearate were pre-expanded in an 11-gallon RodmanSteam pre-expander (Artisan Industries Inc.) at atmospheric pressure.The pre-expansion was operated batch wise. The weight of the cup beads(i.e. 3.5 lbs.) was adjusted to make a pre-puff with a density rangingbetween 2.6 - 3.6 pounds per cubic foot (pcf). The newly preparedpre-puff was air dried for 5 minutes to remove the moisture and wasallowed to age for about 4 hours before molding.

Six-ounce standard cups using different density aged pre-puff beads weremolded. The steam header pressure used was 80 pounds per square inch(psi) and the total cycle time was in the range of 7.50 to 8.25 seconds.The molded cups were allowed to age overnight.

Pre-cut extruded polystyrene film (1.0 mil thick) made from NOVAChemical PS 2110 (general solid polystyrene) resin was fused onto theinner surface of the sidewall of the cups in the same molder used forforming the cups. The header steam pressure used in the film fusionprocess was 45 pounds per square inch and the total cycle time was 5.55seconds. The film-lined containers were stored overnight before testing.

The cups with the varying density pre-puff beads, i.e. 3.47, 3.54, 3.21,and 2.61 pcf, were tested by the following method: Spicy oil at roomtemperature was poured into each container up to around 80% of the cup'sheight. The outside wall of each container containing the spicy oil wasobserved for oil stains and leakage every 10 minutes over the first 1.5hours, every 30 minutes in the time period from 1.5 hours to 6 hours,and, then, every hour up to a total of 48 hours.

The average time failure (ATF) for each cup group sampling wascalculated by adding the time to failure for each container, anddividing the total time by the number of containers tested. Typically,ten cups of each group sampling were tested. The maximum ATF value of 48hours represents that none of the cups for each cup group samplingexhibited any stain or leakage. The minimum ATF value of 0.17 hoursrepresents that all of the cups in each of cup group sampling failedwithin the first 10 minutes.

Each cup in each group sampling was tested for rim strength with andwithout a thermoplastic film and the average force was recorded. Tencups were tested in each group sampling.

The results for the oil retention and the rim strength are shown inTable 1. As indicated in Table 1, the cup samples with the thermoplasticfilm of the invention have an increased ATF and rim strength compared tothe cup sample without the thermoplastic film. TABLE 1 Pre-puff 3.473.54 3.21 2.61 3.47 3.54 3.21 2.61 density (pcf) Film- Yes Yes Yes YesNo No No No lined ATF 48 48 48 48 0.78 0.83 0.83 0.83 (hour) Rim 0.550.57 0.53 0.42 0.29 0.30 0.25 0.19 strength (kg)

Example 2

The oil retention testing and the rim strength testing for cups with apre-puff density of 3.47 pcf were performed in a manner similar to thatof Example 1. These results are shown in Table 2. The polystyrene filmwas similar to that used in Example 1 and its thickness varied as shownin Table 2. As indicated in Table 2, the cup samples with thethermoplastic film of the invention have an increased ATF and rimstrength compared to the cup samples without the thermoplastic film.TABLE 2 Pre-puff density 3.47 3.47 3.47 (pcf) Film thickness 0.0 1.0 1.5(mil) ATF (hour) 0.78 48 48 Rim strength (kg) 0.29 0.55 0.59

Example 3

The oil retention testing and the rim strength testing for cups with apre-puff density of 3.50 pcf were performed in a manner similar to thatof Example 1. The thermoplastic film was similar to that used in Example1 and was either extruded or blown as indicated in Table 3. The volumeof the EPS cups was changed from 6 ounces to 16 ounces. The results areshown in Table 3. The samples with the thermoplastic film fabricated viaan extrusion or a blown process have comparable testing results. Also,the samples with the thermoplastic film of the invention regardless ofthe process for making the thermoplastic film have an increased ATF andrim strength compared to the samples without the thermoplastic film.TABLE 3 Pre-puff density 3.50 3.50 3.50 (pcf) Film thickness (mil) 0 1.01.0 Process of making PS No film Extrusion Blown film ATF (hour) 0.83 3148 Rim strength (kg) 0.35 0.56 0.54

Example 4

In this Example, the polystyrene resin film was replaced with thethermoplastic materials indicated therein. NOVA PS 3500, 4211, 5500, and5102 are the medium and high impact polystyrenes, all of which arediscussed hereinabove. As is indicated in Table 4, the cup samples withthe thermoplastic film fabricated from the different thermoplasticmaterials have comparable ATF and rim strength values. TABLE 4 Pre-puff3.50 3.50 3.50 3.50 density (pcf) Film 1.0 1.0 1.0 1.0 thickness (mil)NOVA PS 3500 4211 5500 5120 resin ATF (hour) 48 38 48 48 Rim 0.56 0.520.49 0.47 strength (kg)

The cups with the fused thermoplastic film of the above Examples have agenerally uniform “rough” or “bumpy” inner sidewall surface. This is duein part to the fact that the film material when fused against thesidewall of the cup covers the voids formed by the expanded polystyrenebeads during the mold processing of the cups and the applied temperaturefor this “fusing” process causes the expanded polystyrene beads toexpand even further.

The thermoplastic container is used for retaining pre-packaged foods,e.g. instant noodles, soups, stews, chicken that are sold on the shelvesin the grocery stores. The container can be placed in the freezer, or inthe microwave for reheating purposes without lessening the integrity ofthe container.

While the present invention has been set forth in terms of specificembodiments thereof, it will be understood in view of the instantdisclosure that numerous variations upon the invention are now enabledyet reside within the scope of the invention. Accordingly, the inventionis to be broadly construed and limited only by the scope and spirit ofthe claims now appended hereto.

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 13. A method for forming a container for holding liquid and/or foods containing oil and/or fatty components, the steps comprising: forming a foam thermoplastic container having a sidewall with an inner surface and an outer surface, and a base with an inner surface and an outer surface, and fusing a thermoplastic film made of thermoplastic resin to at least one of said inner surface and said outer surface of said sidewall of said container to make said container resistant to the penetration of said liquid and/or said oil and/or fat components of said food through said sidewall of said container.
 14. A method of claim 13 wherein said fusing comprises the application of heat at a temperature ranging from about 60° C. to about 120° C. for about 5 to about 20 seconds and the application of pressure to said thermoplastic film ranging from about 20 to about 80 pounds per square inch (psi).
 15. A method of claim 13 wherein said foam thermoplastic container is fabricated via a container machine, the steps further comprising: fusing said thermoplastic film to said one of said inner surface and said outer surface of said sidewall of said container said container machine.
 16. A method of claim 13 the steps further comprising: fusing a thermoplastic film made of thermoplastic resin to said inner surface of said sidewall of said container.
 17. A method of claim 13 the steps further comprising: fusing a thermoplastic film made of thermoplastic resin to said outer surface of said sidewall of said container.
 18. A method of claim 13 the steps further comprising: fusing a thermoplastic film made of thermoplastic resin to said base of said container.
 19. A method for preparing a thin walled container made from expandable polystyrene particles and which container is made to hold liquids and/or foods containing oil and/or fatty components, the steps comprising: pre-expanding said expandable polystyrene particles to a density ranging from about 2.6 to about 3.6 pounds per cubic foot to form pre-expanded polystyrene particles, in a molding process, using said pre-expanded polystyrene particles and further expanding said polystyrene particles to form said thin walled container comprising a sidewall with an inner surface, an outer surface and a rim, and said sidewall having voids formed between said polystyrene particles, and after forming said thin walled container, encircling a thermoplastic film around said inner surface of said thin walled container and fusing said thermoplastic film to said inner surface to cover said voids in said sidewall and to further expand said polystyrene particles to make said container resistant to the penetration of said liquids and/or said oil and/or fat components of said foods through said sidewall of said thin walled container and to improve the strength of said rim of said thin walled container.
 20. A method of claim 19 wherein said thermoplastic film is made of a polymer selected from the group consisting of solid polystyrene, rubber modified polystyrene, polymethyl methacrylate, polypropylene, polyethylene, polyethylene terephthalate (PET), and mixtures thereof.
 21. A method of claim 20 wherein said thermoplastic film has a thickness ranging from about 0.10 mil to about 5.0 mils.
 22. A method of claim 19 wherein said fusing comprises the application of heat at a temperature ranging from about 60° C. to about 120° C. for about 5 to about 20 seconds and the application of pressure to said thermoplastic film ranging from about 20 to about 80 pounds per square inch (psi).
 23. A method of claim 19 wherein said foam thermoplastic container is fabricated via a container machine, the steps further comprising: fusing said thermoplastic film to said one of said inner surface and said outer surface of said sidewall of said container by using said container machine.
 24. A method of claim 19 the steps further comprising: fusing a thermoplastic film made of thermoplastic resin to said outer surface of said sidewall of said container.
 25. A method of claim 19 where said container further comprises a base, and the steps further comprising: fusing a thermoplastic film made of thermoplastic resin to said base of said container. 